1. Field of the Invention
The present application relates to an over-current protection device, and more particularly to a surface-mountable over-current protection device of high-voltage endurance and a circuit board structure containing the same.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37CFR 1.98
With the popularity of portable electronic gadgets, e.g., cellular phones, laptop computers, digital cameras, and personal digital assistants (PDA), over-current protection devices capable of preventing over-current or over-temperature events in secondary cells or circuit devices are becoming increasingly important.
The resistance of a positive temperature coefficient (PTC) device is very sensitive to temperature variation. The resistance of the FTC device remains extremely low at normal temperature, so that the circuit or cell can operate normally. However, when the PTC device heats up to a critical temperature due to an over-current or an over-temperature event occurring in the circuit or cell, the resistance instantaneously increases to a high resistance state (e.g., at least 104Ω), so as to suppress over-current and protect the cell or the circuit device. Therefore, the PTC devices have been widely integrated into various circuitries to avoid over-current damages.
A known traditional SMD over-current protection device for low voltage applications, e.g., less than 32 volts, is small, thin and sophisticated; therefore it uses complex circuit design and is made by PCB processes such as pressing, drilling and copper-plating. As to an over-current protection device of high voltage applications, e.g., larger than 66 volts, it appears relatively large and thick and therefore is suitable for being placed upright or mounted on a circuit board. In order to meet the requirements of high voltage testing, the traditional SMD over-current protection device with compact circuit design may easily induce solder wicking event which causes insufficient isolation, resulting in inferior voltage endurance of the device.